The present invention relates to a structure for sealing the gap between two concentric machine parts which are arranged for linear movement relative to each other, the first machine part being provided with a groove while the second one comprises a plain contact surface arranged opposite the said groove, the sealing ring structure comprising a sealing ring made of a tough-elastic plastic material fitted into the groove and being provided with sealing edges which are arranged adjacent its ends on its first circumferential surface facing the said contact surface and by which it bears against the contact surface of the second machine part, and being further provided with an annular recess arranged in its second circumferential surface facing the bottom of the groove, the sealing ring structure comprising further a stressing ring made of a rubber-elastic material arranged between the said sealing ring and the bottom of the groove, in the recess provided in the second circumferential surface of the sealing ring, the axial extension of the said stressing ring being smaller than that of the sealing ring.
A sealing ring structure of this type has been known from DE-OS No. 36 03 669 in the form of a double wiper arrangement. In the case of this known arrangement, the recess for accommodating the stressing ring is provided at the low-pressure end of the sealing ring and forms sort of a step which is open towards the low-pressure end face of the sealing ring. Accordingly, the stressing ring is retained not only between the bottom of the groove and the second circumferential surface of the sealing ring facing the bottom of the groove, but also between the flank of the groove on the low-pressure end and the flank of the recess facing it at a certain spacing. Under normal operating conditions, the sealing ring is, therefore, retained in contact with the flank of the groove on the high-pressure end, opposite the stressing ring. Further, it is ensured by the particular arrangement that the maximum of the contact pressure of the stressing ring is exerted upon the sealing edge on the low-pressure end.
It has been found in the case of such double wiper arrangements, which simultaneously perform the function of a seal, that increasing pressure on the fluid to be sealed off leads to an increasing leakage rate so that the known arrangement is in any case not suited for use as the sole sealing and wiping element when the fluid to be sealed off is highly pressurized. In such cases, additional sealing elements have to be provided upstream of the described arrangement.